We operationally introduce mixed quantum t designs as the most general arbitrary-rank extension of projective quantum t designs which preserves indistinguishability from the uniform distribution for t copies. First, we derive upper bounds on the classical communication capacity of any mixed t design measurement, for t ∈ [1, 5]. Second, we explicitly compute the classical communication capacity of several mixed t design measurements, including the depolarized version of: any qubit and qutrit symmetric, informationally complete (SIC) measurement and complete mutually unbiased bases (MUB), the qubit icosahedral measurement, the Hoggar SIC measurement, any anti-SIC (where each element is proportional to the projector on the subspace orthogonal to one of the elements of the original SIC), and the uniform distribution over pure effects.